Pulse frequency monitor



M y 1951 s. w. LICHTMAN EIAL 2,553,594

PULSE FREQUENCY MONITOR Filed Feb. 28, 1949 2 Sheets-Sheet 2 m r r0 In} N 10 m :5 a .8

I 2 4 n D a O- N lm 5 m H m n:

E INVENTORS SAMUEL W. LICHTMAN DANIEL G. MAZUR BY ATTORNEY Patented May 22, 1951 v UNITED. STAT-1..

2,553,594 PULSE. FREQUENCY Monrron Samu l W- NT EFECE,

Lichtman and Daniel G. Mazur,

Washington l). C.

amendedAprii, 30, 19283 370 ()j G; 75?) a The presentinventiornrelates in general to a pl lse freqnency monitor for acascadedcounter.

circuit. wherein the counter circuit isperiodically reset by a synchronizing pulse and in particular treeeez cy. men totm y. bei qr c a em If the frequency of thev oscillation generator (counter, drive source) is. lower than the desirejd operating frequency thenumber of drive pulses applied, to. thecounter circuits between synch'ro-- the invention relates to apparatus for detrminnizing pulses Will a co gly be less. than the ing whetherthe frequency of the signal source desired number and Similarly the number O d i in the counter circuit is in accordance with tesh e i u r is nw ll b l s a, .panticular harmonic ordenof the ynchronizing number channelsof transmisslom pulse; the frequency of, the oscillation generator (counj-f Examples counter circuits in which the prester driveTsource) is] high the number. of, drive ent, invention finds application. are disclosed in D 318gg wffil gd ggrggg g sb ig g l U'.,S.' atent tosmith et al.., No. 2,409,229, the c0- 1 9 w pendigg.l application of; Krause et a1., Serial No. han? IQ-desired number, and in a like n 593,174, filed May 11:, 1945;,and in, our co-pendth b r i. ateslt ueh wh ch the n ing application Serial; No. 67,904, filed December 5 ii l f tf l be lleher than the numb r 31 29,1948. ne s o ransin ss on.

Asaparticular illustration of the utility of the. 1,518 fi qm an l ctq t e es i n q i presentiinvention reference i made of our aforeginc gc gifi ghg sti ggg ngf sfi ifigi gi giiisz mentionedco-pending application wherein there em, for'the ransmission an rece ion of a rea t, 1 1 current series of time modulated guises. Each It 15 ?"-x of the i q m ml pulse ofthe series is representativeoi a differ- 9 P u "mf- ,n for f m rfi h j entintelligence channel and its time occurrence f m 1 5 t ma tlme 11,11 withrespect to a reference pulse is modulated in an l; t

accordance with the intelligence it represents. An th QbJect .h Q l n Q 15 The pulse multiplex receiving apparatus of the F m s 1...( leterm1mng c i -i system includes an oscillation generator and a e c e 2 ,3 5? L t cascaded counter chain driven by the oscillation ,3 he?! t it-S 15 generator. The counter chain at the receiver is gig 2 25 55 62 5 5 e pm of frequency F ctlangethe stat? 9 the counter descriptionwhen taken. in conjunction With the synchron sm with the transmission of the several. drawings in which chapngl pulses And-finally each time the coun' I Fig lis a schernatic diagram of a counter cirter chain changes states a timing circuit or other cuit ise bi th pres nt in n 5 device isoperated to time the occurrence of the Fig 2 is a S'hendatic diagram of atypical qnappel mile pulse 40 bQd-iment of. thepresent invention.

1 311198 the mte-lhgence pulses are transmltted" Thepresent invention isbst explained in concyclically h counter chain must start from the V iunction with acascadedcounter circuit such as: 9 otstit-efit the commancemem of each cycle of disclosed in!v the aforementioned patent to C; H! i m This W011 is accomplished Smith. etai.) incorporating the modified embodi; ap n reset/101' syncmonizmg Pulse mentsasdisclosed in our co-pending application, 9. Q 'Q counters m the 7 supra.- It istobe understood however, thatthe; T pulse-returns the t specifieiembodiment' of the present inventionis'f Zero? State and thus permitsl'theoscillatifm notitobelimited to the counter circuitsjdescrihed, generator to s qu ntial v gee Counter moreover, the. present invention may be incor u t and-time sequence as porated. inany system Whereinaserie ofipul'ses. tMQ- r e in timBItO-I thechannels of transarede'rivedffrom. an oscillation generator; and whichseriesef pulsesareperiodically reset by a.

*Ihroughthe 'useof. the reset vpulsethere isprO- reference pulse.

vided ar fer c p in z ro s e f the With particular. reference to Fig.1 a detailed ter -from-which;thepresent. inventiomthe pulse circuit diagram of. the patent to C. H.1Smith,

etc at, incorporating. the. modification. from Your.

co-pending application, is shown. As indicated in the figure, the time base generator comprises an oscillation generator 52, a pulse former 63 arranged to drive a typical counter chain which includes a series of scale-of-two counter stages connected in cascade. The first counter stage comprises two electron tubes 8 and 9. Counter stages 98 and 99 are of similar design. Therefore for purposes or" simplification, only the first counter stage is illustrated in detail. Tubes H3 and i and blocks H through i4 represent the pulse selector tubes with which the time base generator is to operate. The oscillation generator 52 and pulse former 63 may beof any suitable pulse-generating device, such as that shown in our aforementioned co-pending patent application. The primary function of this pulse generator is to provide a source for driving the counter chain through a complete cycle of operation. By interconnection of the control grid of each of the selector tubes to predetermined points in the counter chain, as hereinafter described in detail, the counter circuit is made to successively render each of the selector tubes conducting, during a cycle of operation.

In each scale-of-two counter stage the first control grid 65 of the first tube 8 is connected through the shunt combination of resistance it! and capacitance H to the plate of the second tube 9 and also, through the grid return res'istance it to a source of C potential 89. Likewise, the first control grid 81 of the second tube 9 is connected through the shunt combination of resistance 68 and capacitance 69 to the plate of the second tube 8 and also, through the grid return resistance to a source of C potential 89. The circuit is thus made regenerative and only one of the tubes will conduct at any instant. To change the conduction condition of either tube a negative signal is applied in parallel to the second control grids S4 and 56, of both tubes. As the conduction state of the circuit changes, the first control grid of the tube passing from conduction to nonconduction' will vary from about zero potential to a negative potential determined by the voltage divider action from the positive potential at the plate of the second tube 9 to the negative supply potential across resistances 74, 10.

The input to the counter circuit, as obtained from the pulse former 63, is applied in parallel to the control grids 64 and 66 through a coupling circuit comprising capacitance S5 and resistance 61. In one case this circuit may constitute a short time-constant compared to the time duration of the applied pulse and therefore function to produce an abrupt positive pulse in'response to the positive-goin edge of each of theapplied pulses and an abrupt negative pulse in response to the negative-going edge of each of the applied pulses. The input to the second counter circuit, not illustrated, is taken from a tap on the plate load resistance of the second tube 9 and is applied in parallel through a second short-time-constant circuit capacitance 86 and resistance 8'! to the second control grids oflthe second counter stage. This manner of connecting the counters in cascade is followed through each stage in the series. The quiescent or'zero state for the counter chain exists when tube 8 and all similar tubes in the succeeding counter stages are nonconducting.

In the. selector circuit the control grid of each tube in the series is connected to a separate junction'point I00, 200, and so on. Each of these junction points is in turn connected through separate resistances to the first control grid of the tubes in the counter circuits. This connection is typified at the first junction point E08 by resistances 76, Ti and i8. In this relation it should be noted that all the resistances at each junction point are equal in size and are current limiting in function. At the first junction point HIE) current limiting resistances i6 is connected to the first control grid 65 of tube 8, resistance i?! to the first control grid of the second counter circuit and resistance F8 to the first control grid in the third counter circuit. As above mentioned, the first control grid of any tube in the counter circuit varies from zero potential to a potential determined by voltage division across resistances 14, 10 as that tube passes from conduction to nonconduction. Thus, when the counter is in the zero or quiescent state wherein the tube 8 and the similar tubes in stages so and 99 are conducting, the potential at the junction point lei! will be zero and the selector tube i9 will conduct since its cathode is returned directly to ground.

In our previously mentioned co-pending application there is described a simplified modification eliminating the coincidence tube as described in the C. H. Smith et a1. patent. In our co-pending embodiment each pulse selector stage, such as typified at it and i5, is provided with a separate plate resistor 93 and 8 3, which permits the taking of an output pulse from each stage at points SI and 92, respectively.

There is further provided in the operation of the series of counter stages as disclosed in our copending application a means for cyclically returning each stage to its zereo or quiescent state. This is accomplished by injecting the synchronizing pulse received from the transmitter, over reset pulse input point 32, to the suppressor grid 12 of tube 9. This reset pulse is similarly applied to each stage of the cascaded counter. The reset pulse being of a negative polarity renders tube 9 and similar tubes in stages 98 and 99 nonconducting and hence tube 8 conducting, permitting the counter to repeat its cycle of operation.

Through the use of the reset pulse there is provided a reference point from which our present invention, the pulse frequency monitor 9'? as hereinafter described, may be incorporated. In brief and in accordance with the spirit of our invention the operation of the pulse frequency monitor, for determining the accuracy of the pulse source driving the counter circuit is predicated on the fact that a predetermined number of counter pulses must occur during each synchronizing reset pulse interval. The predetermined number of counter pulses of course is dependent on the number of pulse channels of transmission. As an example, assume for purposes of illustration that there are six channels of time modulated pulses transmitted as illustrated in Fig. 1. There is incorporated in the receiving system a scale-of-six counter circuit for reestablishing pulses, in accordance with the teachings of the aforementioned co-pending application, of a time period analogous to the time period of each channel of transmission.

properly establish the time period of each channel. If the frequencyof the oscillation generator is higher than its proper operating frequency there will accordingly occur atithe output of "the counter circuit more than the. six timing pulses between the twosuccessive synchronizing pulse intervals. Ina similar manner if the oscillation generator frequency is lower than its'proper operating frequency there will-occur at the output of the. counter circuit less than the six timing cillation generator is of the same frequency as the transmitter oscillator and there aresix pulse channels of transmission there will be six pulses in the interval between two synchronizing Pulses. Thepresent invention is ameans for quickly determining the frequency accuracy of the oscillator generator and therefore serves as guides in timing theoscillator. It will also be recognized that the present invention may be employed in determining the frequency of the oscillation generator independentof the counter circuits, wherein a reference point such as a synchronizing pulse is provided.

When the frequency of the oscillation generator is low, the-synchronizing pulse will reset the counter before thelast state in the counter is reached. The present invention provides means for determining the presence or absence of the last counter pulse of the series for determining whether the drive frequency iscorrect or low. When the frequencyof the oscillation generator is high the synchronizing pulse will reset the counter after the first counter state. has been reached for the second time in the normal transmission period. The present invention provides means for determining whether more than one pulse is produced from the first stage in the counter in a given time interval.

Referring in particular to Fig. 2 there is shown a preferred embodimentof the presentinvention which comprises a first series of electron tubes A capable of determining the presence or absence of a single pulse from the last counter stage and second series of electron tubes B capable of distinguishing between one and more than one pulse from the first counter stage.

In operation of the first series of electron tubes A, thelast counter pulse which would normally immediately precede the synchronizing reset pulse, is applied as a negative pulse from terminal 92 through coupling capacitor 24 to grid 51 of tube 2. Vacuum tube 2 and its associated circuit is operative to invert the negative input pulse applied at terminal 92 to a positive pulse. Vacuum tube inverter 2 is operable in a conventional mannerwith plate resistor 35 tied to a point of positivepotential 29, grid 5| grounded through resistor 33 audits-cathode I8 tied directly ,toground. Thepositive pulse from inverter 2 is fed through coupling capacitor 26 to anode 56.0f vacuum tube 3. The output of vacuum tube 3 feeds an integrator operable in a conventional manner for integrating the positive pulse: from vacuum tube circuit 2. The integrated pulse from the output of cathode I 9 is smoothed through capacitor 28 and resistor 30 to give a smooth direct current voltage of a positive polarity.

The smooth direct current voltage of a positive polarity is then applied to grid 53 of vacuum tube 4. Vacuum tube 4 is normally negatively biased 6" with respect :tocathode to nonconduction. Cathode being connected to the center point49 of resistors Hand 46 between B+ and ground, and grid 53 being connected to ground through resistor 42. The direct current voltage derived from the last counter pulse applied to grid 53 is of sufficient positive polarity to overcome the bias applied to vacuum tube 4 to render iit operative. A neon bulb 16, or other-suitable in.- dicating means such as ameter, connectedracross resistor 44 in theplate circuit 5! of vacuum tube 4 will thusly indicate the conduction of the tube and hence the presence of the last counter pulse.

In operation of the second series of electron tubes B, the first counter pulse, the pulse which normally immediately follows the synchronizing tube 1 nonconductivei reset pulse, is applied as a negative pulse from terminal 9: through coupling capacitor- 25 to grid 52 of vacuum tube 5. Vacuumtube5 is connected as a cathode follower operable in a conventional manner for matching the impedance of the input circuit. Its anode 5.8 is tied directly to the point of positive potential 29, and cathode 2| tied to ground through resistor 36. The output taken from cathode 21 of vacuum tube 5 is applied, through coupling capacitor 21 to cathode 22 of vacuum tube 6; Vacuum tube -6 feeds an integrator circuit operable in a conventional manner for converting the negative incoming pulse to a negative direct current voltage. This negative voltage is then smoothed through capacitor 38 and resistor 3| and applied to grid 540i vacuum tube 1. r

The grid 54 of vacuum tube 1 is biased, from point of resistors 41 and 48 between the point of positive potential 29 and ground, in such a manner that a single pulse from terminal 9| is of insufiicient negative voltage to'render vacuum However, if more than one pulse is received during its normal time pe riod, vacuum tube 1 is biased to cut-01f by having a negative voltage applied to. grid 54greater than the positive bias voltage applied thereto. It is seen then that the vacuum tube 1 continues to operate only upon the occurrence of a single pulse. A neon tube H, or a similar device, connected across resistor 43 in the plate circuitof vacuum tube 1 indicates the operation of the tube and hence the presence of one or morethan one pulse.

In summary, if the counter .drive source is of the proper frequency both neon. bulbs I6 and I"! Will be ignited. If the counter drive sourceis low in frequency then bulb l6 will be extinguished and bulb I'l ignited, and finally if thecounter drive source is high in frequency bulb It will be ignited and bulb I! extinguished.

Although we have shown certain and specific embodiments of the present invention, it is to be expressly understood that many modifications are possible thereof.

The invention described herein maybe manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon Or therefor.

What is claimed is:-

1; The combination with a recurrent signal source of a plurality of scale-of-two counter circuits connected in a cascaded chain and fed by said source, means operative to reset said counter chain to a reference state at regular intervals large in comparison to the recurrence rate of said source, means including an integrator fed by the first stage in said chain operative to produce' direct potential output which varies in amplitude dependency upon the number of changes in states of the stage per reset interval, and indicating means fed by said last named means. operative to indicate the presence of an output potential therefrom which exceeds a predetermined level.

2. The [combination with a recurrent signal source of a plurality of scale-of-two counter circuits connected in a cascaded chain and fed by said source, means operative to regularly reset said counter chain to a reference state at regular intervals large in comparison to the recurrence rate of said source, means including an integrator circuit fed by the last stage in said chain operative responsive to a change in state thereof to produce a direct potential output, and indicating means fed by said last named means for indicating the presence or absence of an output potential therefrom, thereby indicating whether said recurrent signal source is in accordance or below a particular harmonic order of said reset means; means including a second integrator fed by the first stage in said chain operative to produce a direct current potential output which varies in amplitude dependency upon the number of changes in states of said first stage per reset interval, and indicating means fed by said last named means operative to indicate the presence of an output potential therefrom which exceeds a predetermined level thereby, indicating whether said recurrent signal source is in accordance or above a particular harmonic order of said reset means.

3. The combination with a recurrent signal source of a plurality of scale-of-two counter circuits connected in a cascaded chain and fed by said source, means operative to reset said counter chain to a reference state at regular intervals large in comparison to the recurrence rate of said source, means including an integrator fed by the first stage in said chain operative to produce a direct potential which varies in amplitude dependency upon the number of changes in states of the stage per reset interval, circuit means fed by said integrator circuit operative responsive to produce an output potential in (16'? pendency on the amplitude of said direct potential derived from said integrating means, and indicating means fed by said last named means operative to indicate the presence of an output potential therefrom which exceeds a predetermined level.

4. The combination with a recurrent signal source of a plurality of scale-of-two counter circuits connected in a cascaded chain and fedby said source, means operative to reset said counter chain to a reference state at regular intervals large in comparison to the recurrence rate of said source, means including an integrator circuit fed by the last stage in said chain operative responsive to-a change in state thereof to produce a direct potential output, circuit means fed by said integrator circuit operative responsive to produce an output potential in accordance with the presence or absence of an output potential from said integrator circuit, indicating means for indicating the presence or absence of an output potential therefrom, thereby indicating whether said recurrent signal source is in accordance or below first stage in said chain operative to produce a direct potential which varies in amplitude dependency upon the number of changes in states of the first stage per reset interval, circuit means fed by said second integrator circuit operative responsive to produce an output potential in dependency on the amplitude of said direct potential derived from said second integrating means and indicating means fed by said last named means operative to indicate the presence of an output potential therefrom which exceeds a predetermined level thereby indicating whether said recurrent signal source is in accordance or above a particular harmonic order of said reset means.

5. The combination of a plurality of scale-oftwo counter circuits connected in a cascaded chain, said [chain having an input terminal for receiving a recurrentsignal, means operative to reset said counter chain to a reference state at regular intervals large in comparison to the recurrence rate of said signal, means including an integrator fed by the first stage in said chain operative to produce a direct potential output which varies in amplitude dependency upon the number Of changes in states of the stage per reset interval, and indicating means fed by said last named means operative to indicate the presence of an output potential therefrom which exceeds a predetermined level.

6. The combination of a plurality of scale-oftwo counter circuits connected in a cascaded chain, said chain having an input. terminal for receiving a recurrent signal, means operative to regularly reset said counter chain to a reference state at regular intervals large in comparison to the recurrence rate of said signal, means including an integrator circuit fed by the last stage in said chain operative responsive to a change in state thereof to produce a direct potential output, and indicating means fed by said last named means for indicating the presence or absence of an output potential therefrom, thereby indicating whether said recurrent signal is in accordance or below a particular harmonic order of said reset means; means including a second integrator fed by the first stage in said chain operative to produce a direct current potential output which varies in amplitude dependency upon the number of changes in states of said first stage per reset interval, and indicating means fed by said last named means operative to indicate the presence of an output potential therefrom which exceeds a predetermined level, thereby indicating whether said recurrent signal is in accordance or above a particular harmonic order of said reset means.

SAMUEL W. LICHTMAN. DANIEL G. MAZUR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,349,810 Cook May 30, 1944 2,389,275 Rayner Nov. 20, 1945 

